1. Field of the Invention
The present invention relates to a fuel supply control apparatus for an internal combustion engine.
2. Description of the Prior Art
In one known fuel supply control method using a programmed microcomputer, the engine running speed and the intake manifold pneumatic pressure are measured with sensors and then used to calculate the basic pulse width of an injection signal to be applied to the fuel injectors. This basic pulse width is corrected in accordance with other engine operating parameters such as the oxygen concentration of the exhaust gases, the coolant temperature, the ambient temperature, and the degree of acceleration. The corrected pulse-width is used to adjust actual fuel feed.
In the preceding method developed by the present applicant, which is not yet known to the art, one-dimensional function tables that give the relationship between the basic pulse width and the intake manifold pneumatic pressure or engine running speed are provided in a storage device beforehand. A basic pulse width corresponding to the detected engine parameters is found from these function tables by interpolation. First, a pulse width TPBSE is found from a one-dimensional function table for the intake manifold pneumatic pressure, and a correction coefficient TPKNE is found from a one-dimensional function table relating the engine running speed. A basic pulse width TP is then calculated by multiplying the pulse width TPBSE by the correction coefficient TPKNE, which corrects for deviations in the intake efficiency of the engine. In other words, the basis pulse width TP is obtained from the equation TP=TPBSE.times.TPKNE.
However, when the above-described method is used, the calculated basic pulse width always has an error greater than ten percent under certain operating conditions, relative to the basic pulse width actually required by the engine. As a result, the controlled air-fuel ratio deviates from the correct value under certain operating condition, causing the exhaust gas purification and other operating characteristics of the engine to deteriorate. In order to avoid such erroneous calculations of the basic pulse width, a two-dimensional function table or more than two one-dimensional function tables must be utilized. However, such a function table or tables complicates the pulse width control program. In addition, such tables take up a great deal of storage capacity.